1. Field of the Invention
The present invention relates to an exposure apparatus used when producing a semiconductor integrated circuit, a liquid crystal display element, a thin film magnetic head, or another microdevice using lithography and to an illumination apparatus which may be applied for such an exposure apparatus.
2. Description of the Related Art
In the lithographic process for producing a microdevice, use is made of an exposure apparatus to transfer a circuit pattern to be formed on a photomask (including reticle) on to a semiconductor wafer, glass plate, or other photosensitive substrate. Further improvement of the resolution is being demanded for improving the integration degree of such microdevices. To meet these demands, exposure apparatuses are being designed which use illumination light of shorter wavelengths such as from the g-rays (wavelength 436 nm) or i-rays (wavelength 365 nm) of mercury lamps to KrF excimer laser light (wavelength 248 nm) or Arf excimer laser light (wavelength 193 nm).
An excimer laser emits pulse light by discharge in a laser medium (gas). The wavelength spectral width xcex94xcex of general excimer lasers is about 500 pm (5xc3x9710xe2x88x9210 m) as shown by the broken line in FIG. 14. When used as the light source of an exposure apparatus, however, it is necessary to narrow the spectral width xcex94xcex to less than about 1 pm as shown by the solid line in FIG. 14 so as to suppress chromatic aberration etc. of the optical lenses mounted in the exposure apparatus.
The wavelength spectral width is narrowed by an optical prism, Fabry-Perot etalon, grating, or other wavelength selection element alone or in combination. The variation in the thus narrowed center wavelength of the laser has to be controlled to as low as xc2x10.1 pm with respect to the reference wavelength.
In this way, the excimer laser light source used for exposure apparatuses inevitably becomes complicated in structure due to the need for control etc. Further, the discharge electrode has to be made longer to make up for the loss of laser output resulting from the narrowing. Accordingly, the excimer laser light source becomes complicated and large in size. The components are also high in price and the running costs high as well.
In general, however, plants manufacturing microdevices install several exposure apparatuses in a clean room. The usual practice is to provide such an excimer laser light source for each exposure apparatus. Each excimer laser light source, as explained above, is complicated and large in size in hardware configuration and is high in initial cost and running costs, so overall a large space is required for the installation of the light sources. This becomes a cause for higher costs as well.
To deal with this problem, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 60-154527, it has been proposed to use a single laser light source and selectively supply laser light for exposure to a plurality of exposure units (exposure stages).
This configuration will be explained in brief with reference to FIG. 16. In FIG. 16, the laser light emitted from a laser light source 51 is selectively sent to a plurality of exposure units 54A to 54D through a light path switch comprised of a light path switching controller 52 and a plurality of mirrors 53A to 53D. That is, the mirrors 53A to 53C are movable mirrors able to be changed in position. The positions of the mirrors 53A to 53C are changed under the control of the light path switching controller 52, whereby the laser light from the light source 51 is guided selectively to one of the exposure units 54A to 54D and used for exposure by the corresponding exposure unit (one of 54A to 54D).
In this configuration, since it is sufficient to provide just a single laser light source 51 for four exposure units 54A to 54D, the configuration becomes simpler, the hardware becomes more compact, and the initial cost becomes cheaper compared with providing a laser light source for each of the exposure units 54A to 54D.
According to this technique, however, since light is supplied from a single light source to a plurality of exposure units, the distance of transmission of the light inevitably becomes longer, it is difficult to maintain the precision of alignment of the optical elements in the light path, and, due in part to this, there is a large loss of light. This problem becomes particularly notable in the case of short wavelength light like KrF excimer laser light of a wavelength of 248 nm or ArF excimer laser light of a wavelength of 193 nm. Therefore, to compensate for this loss, it is necessary to increase the output of the light source. The light source becomes larger in size or shorter in service life and the initial cost and running costs rise.
Further, in a laser light source, even before the end of the service life of the light source as a whole is reached, maintenance such as exchange of the gas or exchange of worn out parts has to be performed periodically or upon need. In the above art, however, since it is necessary for a single light source to provide the pulses used for the plurality of exposure units, the frequently of maintenance becomes high and the time until reaching the end of the service life becomes shorter. Not that great a reduction in the running costs can therefore be hoped for.
Further, since light from a single light source is selectively sent to the exposure units, more than one exposure units cannot simultaneously perform exposure work. Therefore, the throughput (amount of production per unit time) is liable to fall.
In addition, when increasing the number of exposure units so as to increase the production capacity in the above art, the light source itself has to be changed to a higher output one etc. It is structurally difficult to flexibly deal with such changes.
An object of the present invention is to provide an exposure apparatus and illumination apparatus enabling a reduction of size and reduction of costs.
Another object of the present invention is to provide an exposure apparatus able to improve the throughput.
Still another object of the present invention is to provide an exposure apparatus able to flexibly handle changes in the production capacity.
To achieve the above objects, according to a first aspect of the present invention, there is provided an exposure apparatus comprising a single light source for emitting light, a plurality of exposure units for performing exposure using illumination light derived from the light from the light source, a light transmitter having a plurality of light paths for optically connecting the light source and the exposure units, and a plurality of amplifiers, provided in the light paths corresponding to the exposure units, for amplifying the light from the light source.
According to the exposure apparatus of the present invention, since a single light source is provided for a plurality of exposure units and each exposure unit is just provided with an amplifier, but no light source, the overall apparatus is smaller in size and lower in cost. In addition to this, since an amplifier for amplifying the light from the light source is provided corresponding to each of the exposure units, a light source which is low in output, that is, small in size and inexpensive in price, can be used and can be extended in service life.
Therefore, the initial cost required for the light source itself and the running costs can be greatly reduced. Further, since the energy of the light transmitted over the light paths from the light source to the exposure units is small, the optical components (for example, lenses, mirrors, optical fibers, etc.) constituting the light transmitter optically connecting these may be ones of relatively low price and may be extended in service life. The cost can be further reduced by this as well.
Note that some cost is of course required along with the provision of the amplifiers, but amplifiers, unlike light sources, do not need a unit for narrowing the spectral width etc., so are generally inexpensive. The cost can be reduced compared with the rise in cost of the light source, light transmitter, etc. resulting from the use of a large output light source.
Further, according to the present invention, since light is supplied from a single light source to a plurality of exposure units through amplifiers, even if the distance of transmission of the light becomes longer, the loss can be compensated by the amplifiers and there is no need for increasing the output of the light source itself. Therefore, even when using short wavelength light such as KrF excimer laser light of a wavelength of 248 nm or ArF excimer laser light of a wavelength of 193 nm, there is no need to increase the output of the light source so as to compensate for the resultant loss, the increase in size and reduction in service life of the light source can be suppressed, and the cost can be reduced.
While not particularly limited to this, as the light source, it is possible to use an excimer laser, other gas laser, a dye laser, a stationary laser, a semiconductor laser, etc. It is also possible to use a lamp light source other than a laser light source. Further, as the amplifier, an injection locking type excimer laser amplifier can be used.
As the light source, it is possible to use one emitting light of the same wavelength as the illumination light which the exposure units use for the exposure work. Further, as the light source, it is possible to use one emitting light of a wavelength different from the wavelength of the illumination light which the exposure units use for the exposure work. In this case, a plurality of wavelength converters for converting the light from the light source to the wavelength of the illumination light used by the exposure units are provided for the corresponding exposure units. These wavelength converters may be positioned either before or after the corresponding amplifiers.
The light transmitter may be provided with a distributor and the light from the light source distributed equally or unequally to the amplifiers by the distributor. By doing this, one exposure unit can perform exposure work when necessary without regard as to whether other exposure units are performing-exposure work and all of the exposure units can simultaneously perform exposure work in parallel, so the throughput can be improved. This light transmitter, however, may also be provided with a light path switch for selectively sending the light from the light source to one of the amplifiers.
Further, the light transmitter preferably includes optical fiber cables. This is because by transmitting light by an optical fiber cable, the adjustment of the alignment etc. among the lenses, mirrors, and other optical elements for transmitting light becomes simpler, the misalignment of position among optical elements can be reduced, and the loss of light can be reduced. By using optical fiber cables, there is the additional advantage that the freedom of layout of the exposure units can also be improved.
In this case, with a normal optical fiber cable using quartz etc., transmission of short wavelength light like that of a KrF excimer laser (wavelength 248 nm) or ArF excimer (wavelength 193 nm) is generally not possible due to the large loss, but as explained above this can be dealt with by having the light source emit light of a relatively long wavelength (for example, a wavelength of 500 nm or more) able to be sent over this optical fiber cable, transmitting this to near the exposure units using optical fiber cables, and using wavelength converters to convert it to a wavelength of the short wavelength light used by the exposure units.
While not particularly limited to this, the amplifiers may be provided near the illumination optical systems of the exposure units. By doing this, there is almost no distance of transmission of light from the amplifiers to the exposure units, the loss of light can be reduced, and greater efficiency can be achieved.
To achieve the above objects, further, according to a second aspect of the present invention, there is provided an illumination apparatus comprising a single light source for emitting light, a light transmitter having a plurality of light paths for transmitting light from the light source, and a plurality of amplifiers, provided corresponding to the plurality of light paths, for amplifying the light from the light source.
By applying the illumination apparatus of the present invention to an exposure apparatus having a plurality of exposure units, similar actions and effects as the above exposure apparatus of the present invention can be achieved.
To achieve the above objects, according to a still further aspect of the present invention, there is provided an exposure system comprising a master apparatus having a light source for emitting light, a first exposure unit for performing exposure work using illumination light derived from the light from the light source, a first light transmitter having a first light path for optically connecting the light source and the first exposure unit, and a first amplifier, provided in the first light path, for amplifying the light from the light source and a splitter, provided in the first light path, for splitting the light and able to be expanded later by the addition of at least one slave apparatus each having a second exposure unit for performing exposure work using illumination light derived from the light from the light source, a second light transmitter having a second light path for optically connecting the splitter and the second exposure unit, and a second amplifier, provided in the second light path, for amplifying the light from the light source.
As the splitter, it is possible to use a distributor for equally or unequally distributing light to the first amplifier and the second amplifier. Further, as the splitter, it is possible to use a light path switch for switching the supply of light selectively to the first amplifier and the second amplifier.
The splitter may be provided in the master apparatus and disabled before the addition of any slave apparatuses or the splitter may be provided in a slave apparatus and therefore added when adding a slave apparatus.
According to the exposure apparatus of this aspect of the present invention, since a master apparatus provided with a single light source is provided in advance and then one or more slave apparatuses not provided with light sources may be added later together or successively as needed, it is possible to flexibly deal with increases in production capacity. Further, since no separate light source is required at the time of expansion, the cost of expansion can be kept low. Further, since the slave apparatuses are provided with amplifiers, there is no need to change the light source to a high output one along with expansion.